DE102004057957A1 - Turbidity sensor comprises infrared/blue light emitting diode with a luminescence transducer, measuring photo receiver, circuit for the operation in each diode in the pulse process and an analysis circuit signals emitted by the detector - Google Patents

Abstract

The photo receiver emits an intensity-measuring signal for the conception of the light strewn by a sample. The sensor exhibits reference receiver for the determination of the intensity of the radiation of the diodes and a band pass/edge filter in a lighting path of the diodes. The path exhibits a beam splitter in order to decouple a part of the radiation to the receiver. The diode reference light path is extended to the receiver, which is perpendicular to the lighting path.

Description

The The present invention relates to a device for turbidity measurement.

At present, different standards for turbidity measurement exist in different countries as a method for determining water quality. For example, in the European Union, the measurement is required with a monochromatic light source, wherein a diode of suitable wavelength is used as the light source, for example a near-infrared LED according to ISO 7027. On the other hand, the US Environmental Protection Agency (EPA) requires a measurement according to EPA Method 180.1:
with a white light source, wherein the white light source must have the spectrum of a tungsten filament from a predetermined temperature range.

in the In particular, the standards are characterized by the following requirements

ISO 7027:

• • Nephelometric concept
• • 1 Light source with 1 (or more) detectors each at 90 ° angle
• • Wavelength: 860 nm
• • Bandwidth: 60 nm maximum
• • Irradiation Divergence: 0
• • Irradiation convergence: 2.5 ° maximum
• Measuring angle: 90 °
• • measuring aperture: 20 ° -30 ° maximum

EPA Method 180.1:

• • Nephelometric concept
• • 0-40 NTU (higher opacities only over dilution of the medium)
• • 1 Light source with 1 (or more) detectors each at 90 ° angle
• • light source: Tungsten filament lamp with color temperature between 2200 ° -3000 ° K
• • Light path in the measuring chamber: 10 cm maximum
• Measuring angle: 90 °
• • measuring aperture: +/- 30 ° maximum 60 ° total.
• • Spectral measurement window: 400-600 nm
• • measuring cell / cuvette: colorless, transparent, made of glass or plastic

Out The comparison of the two catalogs of demands shows that it apart from the nature of the light source in principle matches gives. In the sense of an increased flexibility and a cost reduction would be It therefore makes sense if a turbidimeter both Meet standards or the basic principles of both standards.

It It is therefore the object of the present invention to provide such a turbidity meter.

to solution This object is achieved according to the invention a simple combination Discarded both measuring principles, instead, the measurement with the White light source as follows modified. Instead of a tungsten filament becomes a white light diode provided, for example, a diode with blue emission and a luminescence converter comprises. Thus, both light sources with operated a largely identical circuit. Especially can Both light sources can be operated in pulsed mode.

The turbidity sensor according to the invention comprises
a first light emitting diode emitting light of at least a first wavelength;
a second light emitting diode emitting light of at least a second wavelength;
at least one measurement photoreceiver for detecting the light scattered by a sample, wherein the measurement photoreceiver outputs an intensity-dependent measurement signal; and
a drive circuit for operating the first and / or second light emitting diode and
an evaluation circuit for processing the primary signal output from the detector.

The Drive circuit preferably comprises a first selection switch with which one of the light-emitting diodes can be selected.

The first light-emitting diode, for example, an infrared LED and the second be a white light LED, which preferably a blue emitting LED with a luminescence converter includes.

The Drive circuit may in particular a circuit for operating a diode in pulsed operation.

Of the at least one measuring photoreceiver can for example, a broadband receiver be.

Of the Turbidity sensor according to the invention can furthermore have at least one reference receiver which determines the intensity of the radiation the first and second light emitting diode detected. In a currently preferred The turbidity sensor according to the invention comprises a first reference receiver for the determination the intensity the radiation of the first light emitting diode and a second reference receiver for Determining the intensity of second light emitting diode.

The turbidity sensor according to the invention comprises in a presently preferred embodiment, a housing which has in its interior at least one chamber which is separated from a media space by at least one window, wherein
the first light-emitting diode and the second light-emitting diode and the at least one measuring photoreceiver are arranged in the at least one chamber,
from the first and the second light emitting diode, a first and a second illumination path in the media space, and
from the media room, a scattered light path to the at least one detector extends.

Of the Stray light path runs preferably perpendicular to the first and second illumination path.

In the first and second illumination paths may optionally have a filter be provided, for example, a bandpass filter in the first illumination path.

Of the first and the second illumination path can each have a beam splitter comprise a portion of the radiation to the first and second reference receiver decouple. equally can directly from the first and second LED reference light paths to the first and second reference receiver, wherein the Reference light paths in a different direction than the illumination paths run. In a currently preferred embodiment the first and second reference light paths are substantially perpendicular to the respective illumination path. A reference signal of the reference receiver is if necessary, the evaluation circuit for normalizing the output signal the at least one measuring photoreceiver supplied. The reference receivers may preferably be selected with a second selection switch suitable for the light-emitting diodes. The second selection switch can be coupled to the first selection switch, dependent on this, or be integrated into it.

The casing may comprise a metallic material, plastic or glass, being with a glass case the windows in one piece with the housing can be trained.

Of the turbidity sensor can be used for example as a submersible sensor in a quiescent medium, or in a streaming Be arranged medium in which the media room or a so-called Measuring chamber is flowed through by the medium.

The Invention will now be described with reference to an embodiment shown in the figure explained.

It shows:

1 a block diagram of a turbidity sensor according to the invention;

2 an unfiltered and a filtered spectrum of a white light diode; and

3 : A sectional view of a turbidity sensor according to the invention.

This in 1 Turbidity meter shown 1 includes for feeding each of a measuring path with white light or with infrared light, a white light diodes 2 which comprises a blue-emitting LED and a luminescence converter to emit white light, and an infrared LED 3 with an emission at 860 nm.

The spectrum of a suitable white light diode is in 2 shown with the dashed line. The luminescence conversion is not complete, so that the spectrum still has a clear maximum in the blue spectral range. Through a suitable edge filter 15 However, the intensity distribution of the white light can be corrected, as shown by the solid line.

suitable White light LEDs are for example from the company Oshino Lamps (Nuremberg Germany) available. Currently, an edge filter from Schott (Mainz, Germany) preferred, which reduces the blue portion of the spectrum.

Near the two LEDs can in each case suitable combinations of diaphragms and / or lenses arranged in each case a sufficiently collimated beam for the measurement paths provide.

The turbidity meter further comprises a sufficiently broadband photoreceiver 4 which can detect both white light and infrared light with sufficient sensitivity. The white light diode is a first reference photoreceiver 5 assigned, which is arranged at the end of a first reference light path, which extends perpendicular to a measuring path of the emitted white light. Likewise, the infrared LED is a second reference photoreceiver 6 assigned, which is arranged at the end of a second reference light path which extends perpendicular to a measuring path of the emitted infrared light.

The measuring photoreceiver 4 and the two reference photoreceptors have, for example, Si photodetectors.

The turbidity meter further comprises a drive circuit 7 , with which either the white light LED or the infrared LED can be operated. The LEDs can be operated in pulse and / or continuous operation. In a currently preferred embodiment, a pulsed operation is provided with a pulse repetition frequency of not more than 10 kHz, preferably not more than 5 kHz, for example about 2 kHz. The duty cycle of each operated LED is about 0.1 to about 0.5, for example, about 0.4. The electrical power for operating the LED, in a presently preferred embodiment, is on the order of about 50 mW to about 100 mW.

The turbidity meter also includes an evaluation circuit 7 with a first signal input, which with the photoreceiver 4 is connected, and a second signal input which is selectively connected to the first or second reference photoreceiver.

To select the respective desired LED and the associated reference photoreceiver are a first selection switch 9 and a second selector switch 10 provided that can be realized in any way. It is advantageous if at least the operation or the activation of the switches is coupled to the extent that false combinations of LEDs and reference photocells can be excluded.

Of the first and the second selection switch can in particular switching transistors which are driven by a microcomputer, wherein the microcomputer is a component of the drive circuit.

As in 3 shown, the aforementioned components are in a housing 15 arranged. The housing preferably has as a material a media-resistant metallic alloy, in particular stainless steel or plastic.

The housing has a concave outer surface portion, which is a measuring chamber 11 outside the housing partially surrounds, in which a medium to be examined can flow.

In the concave surface portion are a first window 12 and a second window 13 provided by which white light from the first LED 2 or infrared light from the second LED 3 into the measuring chamber 11 can be radiated. The first LED 2 and the second LED 3 are with the respective reference recipients 5 . 6 and possibly other optical components such as diaphragms, lenses and filters in a first light source chamber 22 or second light source chamber 23 arranged, in particular with respect to the measuring photoreceptor 4 Sealed to prevent the measurements from being distorted by stray light inside the housing.

The axes of the beam path of the white light and the infrared light are substantially coplanar. They run over a third window 14 which is disposed in the concave surface portion perpendicular to the first and second windows. Through the third window 14 For example, light scattered by the medium can be transmitted to the measurement photoreceiver via a scattered light path defined by diaphragms 4 reach.

The control electronics and the evaluation electronics are in an electronic module 20 integrated, which is a microcomputer 21 for controlling the turbidity meter and the first and second selection switches 9 . 10 includes. The LEDs 2 . 3 , the reference photoreceptor 5 . 6 , as well as the measuring photoreceptor 4 are functionally coupled to the electronics module.

Claims (10)

The turbidity sensor according to the invention, comprising: a first light emitting diode emitting light of at least a first wavelength; a second light emitting diode which emits light of at least a second wavelength; at least a measuring photoreceptor for detecting the light scattered by a sample, wherein the measuring photoreceptor a intensity-dependent measurement signal outputs; and a drive circuit for operating the first and / or second light emitting diode and an evaluation circuit for processing the primary signal output from the detector. turbidity sensor according to claim 1, wherein the drive circuit comprises a first selection switch includes, with which one of the LEDs are selected can. turbidity sensor according to claim 1 or 2, wherein the first light-emitting diode, an infrared LED and the second light emitting diode comprises a white light LED. turbidity sensor according to claim 3, wherein the white light LED comprises a blue emitting LED with a luminescence converter. turbidity sensor according to one of the claims 1 to 4, wherein the drive circuit in particular a circuit to operate each of a diode in pulsed operation. Turbidity sensor according to one of claims 1 to 5, wherein the turbidity sensor continues mindes has a reference receiver, which detects the intensity of the radiation of the first and second light emitting diode. turbidity sensor according to claim 6, wherein the turbidity sensor a first reference receiver for the Determination of intensity the radiation of the first light emitting diode and a second reference receiver for Determination of intensity having the second light emitting diode. turbidity sensor according to one of the claims 1 to 7, wherein the turbidity sensor at least in a lighting path of one of the light-emitting diodes a filter, in particular a bandpass filter or an edge filter having. turbidity sensor according to claim 7, wherein the first and the second illumination path each having a beam splitter about a portion of the radiation to decouple to the first and second reference receiver. turbidity sensor according to claim 7, wherein directly from the first and second light emitting diode Extending reference light paths to the first and second reference receivers, wherein the reference light paths are substantially perpendicular to the respective one Lighting path run.